This invention relates to improving the heat transfer to or from materials flowing in a tube. A typical application for this invention is the high-pressure polymerization of olefins in presence of free-radical-generating initiators in a tubular reactor comprising a series of discrete tubes connected in series.
When materials of high viscosity, such as partially polymerized ethylene, flow through an elongated tubular polymerization reactor, it is difficult to transfer heat to or from them. This difficulty is believed to be caused by fouling of the tube walls with layers of material. A method of improving heat transfer by imparting spiral motion to at least part of the material flowing in the tube is disclosed by U.S. Application Ser. No. 093,017, filed of even date herewith, the entire content of which is incorporated herein by reference. However, it is difficult to inexpensively construct means for imparting spiral motion capable of withstanding the very high forces exerted by materials flowing at high pressure differentials. Furthermore, the force of material flowing past spiral-motion-imparting devices tends to move the devices downstream relative to the tube, away from their original location.
Other difficulties encountered with spiral-flow-imparting device installed within a tube are:
(a) it is not easy to install and remove the devices, which may be necessary to obtain optimum reactor performance under different conditions; PA1 (b) such devices are relatively expensive; PA1 (c) such devices may become part of the tube and, therefore, need to be replaced every time the tube is replaced. PA1 (d) such devices are adversely affected by irregularities in the tube such as eccentricity, varying diameter and lack of straightness; PA1 (e) such devices may be subject to deformation during installation, and, therefore, are incapable of imparting spiral motion in a desired predetermined pattern. PA1 (a) supplying monomer at pressure of at least 15,000 psig to an inlet of a tubular reactor having a length to diameter ratio of at least 500 to 1; PA1 (b) polymerizing said monomer in presence of free-radical-generating initiator at temperature of at least 100.degree. C.; PA1 (c) imparting spiral motion to material flowing through said reactor by flowing the material past a spiral member, said spiral member having maximum length shorter than said tube; and PA1 (d) removing polymer and unpolymerized monomer from an outlet of said reactor. PA1 (a) a spiral member having two ends and a central portion, wherein said central portion has diameter exceeding that of said ends; PA1 (b) a hollow housing snugly fitting over said spiral member, said housing comprising: PA1 (1) The devices are easy to install and remove, allowing ability to adapt to changing reactor conditions caused by, for example, changing products. PA1 (2) The devices are relatively inexpensive to install and remove. PA1 (3) The devices do not become part of the reactor tubing, and hence do not need to be replaced on the relatively frequent occasions when reactor tubing must be replaced. PA1 (4) The performance of the devices is not adversely affected by irregularities in the reactor tubing. PA1 (5) The devices do not change shape during installation, hence they are capable of imparting predetermined spiral motion. PA1 (6) By installing devices of varying configuration, varying degrees of spiral motion may be imparted at different regions along the reactor.